L’étude de la durabilité des polymères renforcés de fibres (PRF) dans le béton est un enjeu majeur de leur développement en tant qu’alternative aux armatures d’acier soumises à la corrosion. La simulation à long terme de la solution interstitielle est le plus souvent assurée par l’immersion des barres de composite dans des solution acides ou basiques, dans lesquelles la température agit comme accélérateur. La littérature propose principalement des analyses physiques et mécaniques des PRF dans leur globalité, sans forcément concentrer l’étude sur chaque composant. C’est donc l’objectif de cette étude de vouloir suivre l’impact des solutions corrosives sur un large panel de matériaux, à la fois sur les résines pures, les fibres, et les composites qui en découlent. Pour cela, des matériaux couramment utilisés en génie civil ont été choisis : deux types de fibres synthétiques (verre et basalte) avec différents agents d’ensimage, trois types de résines thermodurcissables (polyuréthane, époxy et vinylester), et donc six types de composites (3 PRFV et 3 PRFB) fabriqués par pultrusion. Les échantillons ont été conditionnés de façon accélérée à 24°C, 40°C et 65°C dans l’eau et en solution alcaline jusqu’à 10 jours pour les fibres, et entre 2 et 3 mois pour les résines et composites. Des tests physiques et mécaniques ont été menés, tels qu’un suivi de l’absorption d’eau, des mesures de la température de transition vitreuse par DSC, des analyses thermiques et infrarouges et des observations microscopiques. Contrairement à la solution acide, la solution alcaline attaque la fibre de basalte par piquration de façon hétérogène, et aucune espèce chimique n’est dissoute. La durabilité des fibres dans l’alkali dépend de l’agent d’ensimage, une même fibre n’ayant pas le même comportement en traction ni en microscopie selon son traitement de surface. L’eau provoque dans la résine un réarrangement moléculaire visible par DSC, qui ressemble à une plastification irréversible mais qui ne peut pas être une hydrolyse selon l’analyse FTIR. Cela s’explique par la création de deux phases de résine, confirmé dans la littérature par l’observation de deux pics de Tg par DMA, et par la théorie des volumes libres par ATM. La relation de Kelley-Bueche simplifiée permet de conclure que l’absorption de solvant, eau ou alkali, est le facteur critique initiant la dégradation de la résine. Une loi fickienne permet d’approximer la diffusion d’eau dans le polymère et le composite, ce dernier diffusant plus fortement que la résine pure, même lorsqu’aucun vide ou descellement à l’interface n’est constaté. Une interphase aux propriétés modifiées est en fait créée autour de la fibre par l’interaction de la résine avec l’ensimage et l’eau. Une analyse par éléments finis, ainsi que des résultats par AFM et micro-TA de la littérature permettent d’estimer que cette zone diffuse cinq fois plus que la résine pure et mesure entre 1 et 6 micromètres selon les matériaux.

Le sujet de cette thèse est principalement ciblé sur l’étude du transport ionique dans les sulfates d’alcalins de la famille LIMSO₄, où M=Na, K, Rb, Cs. Une attention particulière est portée sur l’étude du système LiNaSO₄, le plus intéressant en termes de dynamique ionique, par RMN en fonction de la température. Dans le cadre de cette étude, nous avons effectué des mesures de temps de relaxation et de largeurs de raie pour toute la série de composés. Des mesures de coefficients d’autodiffusion du ₇li et du ²³Na, ont été menées depuis l’ambiante jusqu’à la température de fusion. Pour la première fois, nous avons pu mesurer la cinétique de transition de phase dans LiNaSO₄, à partir d’une nouvelle méthode basée sur la différence de temps de relaxation dans les deux phases de part et d’autre d e la transition, mais sans mesurer forcément le T₁. Cette technique élaborée dans le cadre de ce travail permet de mesurer l’évolution au cours du temps du volume de la phase qui apparait pour des vitesses de refroidissement contrôlées. Nous avons aussi mené une étude par RMN des réorientations des groupements sulfates dans la phase basse température. L’influence des réorientations des SO ₄² sur les couplages quadripolaires au noyau 7li, a été étudiée par un modèle de réorientation par sauts, qui n’avait encore jamais été utilisé pour les sulfates. La méthode proposée est une méthode à « bas couts » car elle permet d’atteindre l’information sur la dynamique des groupements sulfates sans enrichir l’échantillon en ¹⁷O ou de mener des expériences très longues pour le ³³S, ou sans passer par les mesures de temps de relaxation. Afin d’analyser le rétrécissement par le mouvement (motional narrowing) en fonction de la température dans les solides avec deux sous réseaux cationiques diffusant comme dans le cas du LiNaSO₄ , nous avons élaboré un modèle permettant de fitter l’évolution observée à deux marches de la largeur de raie RMN avec la température. La fonction analytique obtenue a été étendue au cas de distributions de temps de corrélation. / The main goal of a present research is a detailed study of ionic transfer in double sulfates belonging to the LIMSO₄ family, where M = Na, K, Rb, Cs. The most attention has been paid to LiNaSO₄ as to the most interesting (in terms of the ion dynamics) compound among other double sulfates. We have carried out magnetic relaxation measurements and line width analysis for all compounds under consideration. Moreover, PGF NMR measurements of ₇li and ²³Na self-diffusion coefficients in LiNaSO4 have been carried out. For the first time, we have measured the phase transition kinetics in LiNaSO₄. For this purpose, we developed a new technique, which is based on the difference of spin-lattice relaxation times in the two phases, but which does not involve the direct measurement of T₁. Elaborated technique allows measuring time evolution of the volume of the appearing phase at controlled cooling rates. We have carried out NMR study of the sulfate ion reorientations in the low-temperature modification of LiNaSO₄. The influence of the SO ₄² reorientational jumps on the quadrupolar interactions of 7Li nuclei was investigated b y a j ump reorientational model, which has not previously been app lied to sulfates. The proposed method is a “low-cost” technique, since it does not require an ¹⁷O enriched sample and dispenses with time-consuming ³³S NMR. Other advantage of a given method is a possibility to probe reorientational motions without NMR relaxation measurements. To analyze motional narrowing in solids with two diffusing spin sublattices (such case occurs, e.g., in LiNaSO₄) we deduced a formula, which can be used for fitting of the two-step temperature dependencies of the NMR line width. The obtained function has been al so ex tended to the case, when a distribution of correlation times takes place. The advantage of this approach is that even in the case of distribution of correlation times, the fitting function could be expressed in the analytical form.

Abstract In this work, evolution of structural properties of anhydrous and hydrated alkali halide clusters are studied using synchrotron radiation based photoelectron spectroscopy. Alkali metal core level spectra of small anhydrous RbCl, RbBr, CsCl and CsBr clusters indicate a NaCl structure. For larger CsBr clusters a structural phase transition to CsCl structure is likely the case. Alkali halide core level spectra of mixed RbBr-water clusters indicate that at dilute concentration the salt is dissolved by the water cluster but ion pairing increases with concentration. Modeling of gas phase cluster formation and electronic structure calculations of core level chemical shifts are used to interpret the experimental spectra.

L'optimisation de la composition des vitrifiats de REFIOM en les rendant alcali-résistants en vue de leur conférer une bonne durabilité chimique en milieu alcalin pour être ensuite utilisés dans les matrices cimentaires a été étudiée. La méthodologie suivie consiste à étudier le comportement à la lixiviation en mode statique de verres modèles alcali-résistants de type CEMFIL et de vitrifiats de REFIOM auxquels on a rajouté SiO2, Na2O et ZrO2 pour leur conférer un caractère alcali-résistant. Les tests de lixiviation menées à 90°C et à différents temps (de 6 heures à 28 jours) ainsi que les autres techniques d'analyse chimique (ICP-AES, MEB-EDS, SIMS, ERDA, RBS, PIXE) sur ces verres ont montré que ce sont les vitifiats de REFIOM dont la composition a été optimisée qui présentent la meilleure durabilité chimique quelque soit le pH / The main goal of this research work is to optimize the composition of vitrified REFIOM into alkali-resistant glasses in order to enhance their durability and in alkaline media. The expected industrial application deals with the use of these glasses associated with concrete in composite materials. The experimental approach is based on static leaching tests of model alkali-resistant glasses and vitrified REFIOM in witch we have added SiO2, Na2O et ZrO2 in order they become alkali-resistant vitrified REFIOM. The leachates have been analysed by ICP-AES and the solid surfaces characterized by scanning electron microscopy, electron microprobe analysis, secondary ion mass spectrometry depth profiling, and synchrotron radiation spectroscopies. All those analysis showed that alkali-resistant REFIOM are the best durability in every media

This study seeks to focus on the total female experience of African women and the reappropriation of a more authentic portrayal of the identity of women in African literature. In this dissertation, a chapter is devoted to each of the female protagonists in the three novels selected for discussion which are One is Enough (1981) by Flora Nwapa, Second-class Citizen by Buchi Emecheta (1975) and The Stillborn (1988) by Zaynab Alkali. Each chapter is named after the woman whose transformation it explores and the chapters are organised in a chronological sequence, that is, in the order that the writers of the texts were first published as authors of African literature, rather than according to the publication date of the text under discussion. The mode of treatment of the texts is dictated primarily by the womanist thrust and the central question of the way in which each of the female characters transcends the triple jeopardy of colour, class and gender to become a creative non-victim. The epithet 'creative transformation' in the title, therefore, describes the emergence of female characters in African writing who overturn the literary characterisation of the one-dimensional African woman who is a 'shadowy figure who hovers on the fringes of the plot, suckling infants, cooking' and 'plaiting' hair {Frank, 1987:14). The theoretical approach adopted for this study is largely of an eclectic nature but every effort has been made to establish a strong sense of the authenticity and credibility of the African woman's experience. In other words, the three texts chosen have been treated as both essentially social realist and African feminist texts read from a womanist perspective. The term ‘womanist’ is particularly valuable in the context of this study. The definition of womanism used in this study is that forwarded by critics such as Chikwenye Ogunyemi (1985) who states that ‘womanism believes in the freedom and independence of women like feminism’ but that ‘unlike feminism’, womanism ‘wants meaningful union between women and men and will wait for men to change their sexist stance’. The findings of this study show that the female protagonists achieve transformation not by reforming patriarchal systems, but by being creative and reappropriating their own identities within these often antagonistic systems. That is, the women achieve a measure of fulfillment and a strong sense of their own individuality within an imperfect context. Particularly in their individual responses to the experiences of marriage and motherhood in a traditional context and in their seeking an authentic identity, the characters in the novels studies create a framework that enables them to be the women they want to be and not the women society would like them to be: Amaka bears twins fathered by Izu, a Catholic priest; Adah – a mother of five – leaves a violent relationship to pursue a career as a writer and Li, after establishing an independent academic life, returns to her errant husband in the hope that they can rebuild their life together. / Dissertation (MA (English))--University of Pretoria, 2007. / English / unrestricted

Density Functional Theory (DFT) is an effective tool for studying diverse metal systems. Presented herein are studies of a variety of metal systems, which can be applied to accomplish transformations that are currently difficult/impossible to achieve. The specific topics studied utilizing DFT include: 1) C–H bond activation via an Earth-abundant transition metal complex, 2) C–H bond deprotonation via an alkali metal superbase, 3) and amination/aziridination reactions utilizing a CuI reagent. Using DFT, the transformation to methanol (CH3OH) from methane (CH4) was examined. The transition metal systems studied for this transformation included a model FeII complex. This first-row transition metal is an economical, Earth-abundant metal. The ligand set for this transformation includes a carbonyl ligand in one set of complexes as well as a phosphite ligand in another. The 3d Fe metal shows the ability to convert alkyls/aryls to their oxidized counterpart in an energetically favorable manner. Also, “superbasic” alkali metal amides were investigated to perform C—H bond cleavage. Toluene was the substrate of interest with Cs chosen to be the metal of interest because of the highly electropositive nature of this alkali metal. These highly electrophilic Cs metal systems allow for very favorable C—H bond scission with a toluene substrate. Finally, the amination and aziridination of C–H and C=C bonds, respectively, by a CuI reagent was studied. The mechanism was investigated using DFT calculations. Presently, these mechanisms involving the use of coinage metals are debated. Our DFT simulations shed some insight into how these transformations occur and ultimately how they can be manipulated.

This thesis deals with development of shrinkage reducing admixtures designed for alkali activated materials based on blast furnace slag. The main task of this work is to select the most suitable shrinkage reducing admixture based on experiments, in which can be observed minimal shrinkage and at the same time it will not adversely affect the properties of alkali activated blast furnace slag. In the experimental part of the work, test beams containing shrinkage reducing admixtures were prepared, in which the shrinkage and loss of weight were measured. Moreover, the mechanical properties of individual beams, such as tensile strength and compressive strength, were measured. Next, the surface tension of individual shrinkage reducing admixtures was measured in a mixture with pore solution. The hydration process of alkali activated materials under the action of reducing shrinkage admixtures was monitored by calorimetric analysis. The microstructure of the prepared samples was observed by scanning electron microscopy.

Alkali-activated materials (AAM) are construction materials with great potential, especially for their environmental friendliness, but also due to their mechanical properties. Therefore, it is appropriate to pay further attention to these binders. This diploma thesis deals with monitoring the effectiveness of plasticizers in connection with the surface chemistry of the alkali-activated slag system. Sodium hydroxide and sodium water glass were used as alkaline activators for the preparation of alkali-activated blast furnace slag-based systems. To study the effectiveness of the lignosulfonate plasticizer, yield stress, heat flow, adsorption and zeta potential were monitored depending on the amount and time that the plasticizer was added to the system. The results show that the type of activator used in the mixtures plays an important role. NaOH-activated samples revealed the best efficiency of lignosulfonate plasticizers. A key factor in studying the behavior of the studied mixtures was the measurement of the zeta potential, which provided insight into the surface charge of blast furnace slag particles related to the ability of lignosulfonate to adsorb on grains of alkali-activated slag.

Combination of fine ground granulated slag with proper alkaline activator gives alkali-activated slag – a material with remarkable properties. Theoretical part of the thesis deals with summarizing basic informations about alkali-activated slag, its properties, production and utilization. It also follows research devoted to effects of curing of alkali activated slag and shrinkage-reducing admixtures on its properties. Objective of the experimental part is to determine the influence of curing conditions on the mechanical properties and microstructure of alkali-activated slag. These properties are also monitored in alkali-activated slag with carbon nanotubes and hydroxypropylmethylcellulose as an shrinkage-reducing admixtures.

Ground granulated blast furnace slag is a by-product of the steel industry and is often used in combination with ordinary Portland cement as a binder in concrete. When concrete is exposed to high temperatures, physical and chemical transformations lead to significant loss of mechanical properties. This study aims to investigate the effect of high temperatures and rehydration on the mechanical properties, microstructure and phase composition of alkali activated slag. The results of the research could make an important contribution to decisions made concerning the reconstruction of structures affected by fire. In suitable cases it would be possible to regenerate parts of a structure instead of totally rebuilding it.